Why Cary Grant’s sunglasses in North by Northwest still make us swoon.

When Cary Grant first dons his sunglasses in Alfred Hitchcock’s North by Northwest, he’s hiding, rather unconvincingly, from the police at Grand Central Station. When he takes them off, he is successfully propositioning Eva Marie Saint for sex in a train dining car. The intervening five minutes of film show Grant in great peril and distress—but through it all, he remains completely, impossibly cool. Not just because of his wit, or his sex appeal, but because of his sunglasses, the coolest article of clothing in history: Vintage Tart Arnels. [Update, Oct. 16, 2013: Perhaps they are not vintage Tart Arnels! But what are they?]

Coolness is, of course, a frustratingly ineffable quality; you know it when you see it, sure, but sometimes it’s impossible to explain what you’re actually seeing. And so it is with Cary Grant, an actor who remains archetypally cool despite a number of qualities—the unplaceable accent, the too-bronze skin—that should seem hackneyed or hokey today. So it is with his sunglasses in North by Northwest: With their tan plastic tortoiseshells and green-tinted lenses, the Tarts could seem a little dorky. But Grant’s insouciant charisma transfigures them into the quintessence of cool.

Consider the dining car scene. Saint has just saved Grant, who has been wrongly accused of murder, from arrest. He’s slightly flustered, and the sunglasses seem, for an instant, like little more than a silly disguise. But as he sizes up Saint and his face settles into sly detachment, the Tarts suddenly become a tool of seduction, magnifying his sardonic wit and perfectly framing his classically handsome face. The two soon settle into easy banter (verbal foreplay, really) over a meal, and Grant, still Tarts-clad, subtly switches gears. A few minutes earlier, he had been in total control, but now he gives a bit of ground, performing a delicate dance with the Hitchcock blonde. Saint teases Grant about the Tarts—“Is there something wrong with your eyes?” The two exchange coy glances and arch quips, and Grant slowly removes his sunglasses, revealing the twinkling eyes beneath. He holds them in his hands while lingering on a remark. Then, after a brief back and forth, he goes in for the kill:

“The moment I meet an attractive woman,” he admits, “I have to start pretending I’ve no desire to make love to her.”

“What makes you think you have to conceal it?” Saint answers.

Grant smiles and puts away his sunglasses. Their work here is done. The two go back to Saint’s sleeper.

With his Tarts off, Grant was an urbane charmer, a droll movie star. But with his Tarts on, he was something more. Even today, the Tarts feel risky: Their light brown rims could easily seem cheap and flimsy, their wide frames inelegant and unusual. This daringness, though, is the crucial to their coolness. During the sunglasses scenes of North by Northwest, Grant is essentially on the prowl, slinking past police officers and onto a train, pouncing on a woman who seems open to sex. In classically cool sunglasses—Wayfarers, for instance—Grant would have simply been trying too hard. In green-tinted, tan-rimmed Tarts, he doesn’t appear to be trying at all.

Throughout his career, Grant proved that he could maintain his cool through pratfalls and Nazi plots, love triangles and jewel heists. But he would never be cooler than those few minutes on a train with Eva Marie Saint, drinking cocktails and discussing love, wearing sunglasses that seduced us as effortlessly as he seduced her.